The field of molded optics has been the subject of extensive research in recent years. Thus, the practice has the great advantage in permitting lenses to be molded that are difficult to manufacture utilizing conventional grinding and polishing methods. For example, U.S. Pat. Nos. 4,093,469 and 4,098,596 disclose the reshaping of a preform of hydrosilicate glass, i.e., a glass containing a substantial amount of water in its structure, into a lens via compression molding. The surface of the lens replicates the mold surface and is equivalent to a ground and polished optical surface.
The use of hydrosilicate glasses as precursor materials in molding shapes has several practical disadvantages. First, the glass composition must be relatively readily subject to hydration; hence, the range of operable compositions and the resulting properties of the final product are quite limited. Second, the glass must be subjected to a hydration treatment. Third, extremely careful control of atmosphere must be exercised during the molding operation. Accordingly, glasses which can be molded or otherwise shaped under pressure at relatively low temperatures, i.e., temperatures below about 450.degree. C. and preferably below 400.degree. C., without the need for hydration could prove to have high utility. It would be necessary, of course, for such glasses to demonstrate the basic practical characteristics found in more conventional glasses such as, for example, good glass quality coupled with reasonable chemical durability and stability against devitrification.